TRIGGERED STAR FORMATION IN GALAXY PAIRS AT z=0.08-0.38

We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z = 0.08-0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9825 Smithsonian Hectospec Lensing Survey galaxies with R <20.3. To examine the evidence for tidal triggering, we identify a volume-limited sample of major (vertical bar Delta MR vertical bar < 1.75, corresponding to mass ratio > 1/5) pair galaxies with M-R < -20.8 in the redshift range z = 0.08-0.31. The size and completeness of the spectroscopic survey allow us to focus on regions of low local density. The spectrophotometric calibration enables the use of the 4000 angstrom break (D(n)4000), the H alpha specific star formation rate (SSFRH alpha), and population models to characterize the galaxies. We show that D(n)4000 is a useful population classification tool; it closely tracks the identification of emission line galaxies. The sample of major pair galaxies in regions of low local density with low D(n)4000 demonstrates the expected anti-correlation between pairwise projected separation and a set of star formation indicators explored in previous studies. We measure the frequency of triggered star formation by comparing the SSFRH alpha in the volume-limited sample in regions of low local density: 32% +/- 7% of the major pair galaxies have SSFRH alpha at least double the median rate of the unpaired field galaxies. Comparison of stellar population models for pair and for unpaired field galaxies implies a timescale for triggered star formation of similar to 300-400 Myr.